This invention relates to certain novel zirconium compounds of sulfonic acids. More particularly, it relates to zirconium compounds of substituted (functionalized) and unsubstituted mono- , di- , and polysulfonic acids.
The novel compounds of this invention are useful as recyclable catalysts for various organic chemical reactions, as, for example, in the production of esters and polyesters.
There is a general need in industry for recyclable catalysts with good catalytic activity. Good catalytic activity is often obtained with soluble catalysts (i.e., compounds soluble in the reaction medium), but such catalysts can be difficult to remove from the final product. Soluble catalysts always present a potential product contamination problem, and soluble catalysts must often times be washed out of products which can't be distilled (away from the catalyst). Recyclable catalysts are environmentally friendly, as recycling reduces the (total) amount of material requiring disposal. The catalysts of this invention can be used as mostly insoluble solid (recyclable) catalysts for the production, for example, of esters by either direct esterification or transesterification. Other solid (recyclable) catalysts have been used in esterification, but such catalysts (e.g. ion-exchange resin catalysts--Amberlyst.RTM. 15) generally have use temperature limitations (approx. 100.degree.-110.degree. C.). The zirconium compounds of this invention, when compared to ion exchange resins, generally have an extended range of permissible operating temperatures.
Zirconium methanesulfonate has an advantage over other common transesterification catalysts, such as tetrabutyl titanate and zirconium acetyl acetonate, in that it is not deactivated by the water sometimes present in the ester/alcohol reactants. Many common transesterification catalysts require anhydrous reaction conditions (i.e., predried reactants), and the manufacture of esters using such catalysts requires an additional drying step in the preparation process. For the preparation of propyl propionate via transesterification of methyl propionate with 1-propanol, the water sensitivity of common transesterification catalysts is clearly shown by plotting the % propyl propionate formed versus time for reactions employing dried and undried reactants with a variety of common catalysts--(See FIG. 1 of the drawings).